Recessed spring washer flow drill screw

Abstract

A screw for use in joining workpieces, for example automotive body parts, is provided that includes a head portion, an externally threaded shank extending from the head portion, a flow-hole-forming tip disposed at a distal end portion of the externally threaded shank, and a recessed spring washer disposed under the head portion. The recessed spring washer is configured to apply a clamping load to joined workpieces as they expand and contract.

What is claimed is: 
     
       1. A screw comprising:
 a head portion; 
 an externally threaded shank extending from the head portion; 
 a flow-hole-forming tip disposed at a distal end portion of the externally threaded shank; and 
 a recessed spring washer defining a flange having a flat distal face and disposed under the head portion with a spring rate sufficient to prevent torque fall-off and deforms with application of torque to the head portion. 
 
     
     
       2. The screw according to  claim 1 , wherein the recessed spring washer is integrally formed with the head portion. 
     
     
       3. The screw according to  claim 1 , wherein the head portion defines a tool engagement feature. 
     
     
       4. The screw according to  claim 1 , wherein the recessed spring washer is a different material than the head portion, externally threaded shank, and the flow-hole forming tip. 
     
     
       5. The screw according to  claim 1 , wherein the flange of the recessed spring washer extends at least 90° from a longitudinal axis and a proximal end portion of the screw. 
     
     
       6. The screw according to  claim 1 , wherein the screw is a material selected from the group consisting of boron steel and 7000 series aluminum. 
     
     
       7. The screw according to  claim 1 , wherein the screw defines regions of varying hardness. 
     
     
       8. A screw comprising:
 a head portion; 
 an externally threaded shank extending from the head portion; 
 a flow-hole-forming tip disposed at a distal end portion of the externally threaded shank; and 
 a recessed spring washer disposed under the head portion, the recessed spring washer defining a flange having a flat distal face so as to maintain an improved seal between the flange and a workpiece, the flange extending at least 90° from a longitudinal axis and a proximal end portion of the screw, 
 wherein the recessed spring washer defines a spring rate sufficient to prevent torque fall-off and deforms with application of torque to the head portion, thereby applying and maintaining a load workpieces being joined by the screw. 
 
     
     
       9. The screw according to  claim 8 , wherein the screw defines regions of varying hardness. 
     
     
       10. An assembly comprising:
 a plurality of workpieces; 
 a screw disposed between the workpieces comprising: 
 a head portion; 
 an externally threaded shank extending from the head portion; 
 a flow-hole-forming tip disposed at a distal end portion of the externally threaded shank; and 
 a recessed spring washer defining a flange having a flat distal face and disposed under the head portion with a spring rate sufficient to prevent torque fall-off and deforms with application of torque to the head portion. 
 
     
     
       11. The assembly according to  claim 10 , wherein the workpieces are a material selected from the group consisting of aluminum, polymers, and polymer matrix composite material. 
     
     
       12. The assembly according to  claim 10 , wherein the recessed spring washer of the screw defines a flange extending at least 90° from a longitudinal axis and a proximal end portion of the screw. 
     
     
       13. The assembly according to  claim 10 , wherein the recessed spring washer is integrally formed with the head portion. 
     
     
       14. A motor vehicle comprising the assembly according to  claim 10 .